Electric transformer



Feb. 26, 1929 1,703,410

F. s. SMITH ELECTRI C TRANSFORMER Filed March '7, 1922 2 Sheets-Sheet lINVENTOR ATTORNEY Feb. 26, 1929. 1,703,410

F.5 SBVTH ELECTRIC TRANSFORMER Filed March 7, 1922 2 ShetS-Sheet 2sNvENToR Y ATTORNEY Patented Feb. 26, 1929.

UNITED STATES PATENT *'oFFicE.

FRANKLIN S. SMITH, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO THE PROD-UCTS PROTECTION CORPORATION, OF NEW YORK, N., Y., A CORPORATION OF4DELAWARE.

ELECTRIC TRANSFORMER.

Application led March 7', 1922. Serial N'o. 541,749.

My invention relates to electric transformers, particularly the highvoltage windings thereof and the means for supporting and insulating thesame, and it has for one of itsv objects to provide anovel andthoroughly practical construction wherebyv a fluid dielectric andcooling medium within the tank of the transformer is brought, in asimple, de-- pendable and efficient way, in contacting` or impingingrelation to the metal'of the windings of the transformer for the purposeof lowering the temperature gradient between the windings and thecirculating cooling medium. The mechanical features of my conr structionare particularly well suited and adapted for use in connection with agaseous dielectric and cooling medium under pressure i greater thanatmospheric pressure, and in such coacting relation I achieve manythoroughly practical and important advantages.

Another object of the invention is to provide a solid dielectric forassociation with the high voltage winding in which the parts employedare of a character that can be readily V standardized and may be readilymolded or stamped and formed, thereby facilitating quantity production.

Another object of the invention is to provide a high voltage transformerconstruction in which the dielectric strength between turns of the hightension winding between coils, between the end coils and core,bet'weenthe high and low voltage windingsfand between the winding and coie ismuch greater r than heretofore has been attained, as far as I am aware,in any transformer structure of like volume, capacity and voltage.

Other objects are to provide a high voltage winding structure in whichthe coils yare spaced and supported= by solid dielectric parts ormembers of such configuration. that the said solid dielectric is inseries with fluid dielectric iii the path of higher' voltage gradi- Fcnt, and in which the path of surface leale age on said solid dielectricis in a path lower voltage gradient.

Other objects will be in part obvious or in part pointed outhereinafter. l

The invention accordingly consists in the features of construction,combinations of elements, and arrangements of parts as will be lexemplified in the structure to be hereinafter described and the scopeof the application of which will. be indicated in the following claims.

In order that the invention may be readily understood and its advantagesfrom a practical standpoint fully appreciated, 'reference may be had tothe accompanying drawings in which certain convenient forms ofembodiment thereof are shown.

In the drawings:

Fig. 1 is a view partly in top plan and partly in transverse sectionshowing certain mechanical featurescf a transformer embodying myinvention, taken on the line 1-1 of Fig. 2;

Fig. 2 is a view partly in elevation and partly in central verticalsection; Fig. 3 is a view partly in plan and partly in transversesection taken on the line 3-3 of Fig. 4 depicting a modified form oftransformer construction embodying the invention;

Fig. 4 is a View partly in elevation andl partly in central verticalsection of the transformer shown in Fig. 3; and

Fig. 5 is a fragmentary view of a portion of a coil of a high voltagewinding showing y may be and preferably is built up of suitablelaininations, as is clearly shown in Figure 1, and. may be of anysuitable form or shape; conveniently and illustratively I have shown thecore 4 to be of the shell type and accordingly it has two verticallyextending legs 4 and 4b joined by the horizontal or transverselyextending portions 4c and 4B, with a middle or central verticallyextending leg 4 joining the portions 4 and 4. About the middle leg 4tare the windings. The low voltage winding 10 is wound upon a tubularsolid dielectric support 11 which incloses the central leg/1t of thecore and is supported upon or by the said core. The adjacent turns(clearly shown p as indicated at 12 in Figure 1, are formed,

and these are preferably also utilized, as will be made more clearhereinafter, in the circulation of thefiuid dielectric and coolingmedium which, as above ynoted, .is preferably a gas under pressuregreater than atmospheric` the transformer in the path offhigher voltageFor the purpose of supporting the coils of the high voltage'winding ofthe transformer, l have provided a support eon'iprising the tubular partor section 15 of solid dielectric material having at its lower and upperends outwardly-extending annular disks 25 and 26 of solid dielectricmaterial which are arranged substantially at right v angles to lthe axisof the said tubular part or section 15. These disks are each providedwith annular flanges at their inner edges which titl closely against theouter lower and upper surface portions of the tubular part 15 and aresecured thereto. Preferablyv the said tubular part or section 15 .andthe horizontally extending annular disks 25 and 26 are formed of moldedbakelite or of bakelized paper, hot pressed.

l However, it will be understood that theseparts may be constructed ofother suitable material. y y

The high tension winding is preferably made up of a plurality of coils20 extending about the tubular insulating; member 15 and hence about thecentral leg 4f of the core; the coils 20 are spaced-from one another inan axial direction byparts 16` which are situated between the adjacentcoils of the high voltage winding. The parts 16, which I shall forconvenience designate as (washers, are of sinuous form, as is clearlyindicated in the several figures of the drawings, so that the oppositeyedges of the wires of vthe coils -20 touch the washers at intervalsonly. The sinuous parts 16 of solid dielectric are in series with thefluid dielectric within'the tank (not shown) of gradient while theleakage along the `surface of the said solid dielectric between theVpoints of contact thereof with the opposing coils is in a path of lowervoltage gradient. This is due to the fact that the annular parts 16 ofdielectric material, previously referred to as washers', are ofcorrugated or sinuous formation so that the points of contact of oppsingsides oredges of adjoining coils 2O with an interposed washerarearranged in staggered relation to each other, as shown in Fig. 2. Byreason of such relationship it is apparent that the leakage betweenadjoining coils along the said interposed washer of dielectric materialmust be along inclined paths which are of greater length than thevertical vdistance between the said coils with the result that therelation -of the voltage gradients is as just stated. The inner tubularportion or part 15 of the support for the high voltage windings isprovided with perforations through which the Huid dielectric and coolingmedium, preferably gas, may pass. 'lhese perforations, in theconstruction shown, are circular and may be regarded asVv arranged ingroups of three, the axes of the perforations of each selected groupbeing located withrespect lto each other at the three corners ofequilateral triangles. The diameters of the perforations lare-of suchlength that a line drawn from a point outside of any such group ofopenings cannot pass straight through such group without vcutting atleast oneof vthe perfolations. It follows, therefore, that'the leakagealong lthe surface of the tnbe'15`cann0t be in straight paths or lines.'It is to be understood, however,l that perforations of otherconfiguration and lrelative position may be employed.

The bottom .coil of thehigh voltage winding is supported upon the upperside of the annular disk 25 of solid'dielectric while-the bottom side ofthe disk 26 contacts with the top edges of the uppermost of the coils ofthe high voltage winding.

Theopposite edge portions of the 'flat wire of the high vltagecoils arebare and rounded, and the opposite .sides thereof are coated withenamel, or .may be-spaced or separated by bakelized paper or othersuitable material. f

The high voltage winding' structure is supported from the cross-Wiseextending angle iron members 2 at vthe upper part of the core `:tructureand angle iron members 3 at the bottom part of the'core structure` bymeans of X-shaped 1 mbers-30 and 31. The ends of the bars on one side ofthe X-shaped members 30 and 3l are secured to the horizontal flanges ofthe angle' ironl members 2 and 3 respectively, while the ends of fthesaid bars at the oppositeI sides of said X-shaped members areinengagement with the outer faces of the disks 25 and 26.' In order toprevent displacement lateralrly of the-disks-Q and 26 with respect to:the supports 3() and .31 vthe disks are provided with raisedportions 32veachof which. has a recess 33 therein into which `the, ends of the barsat the inner sides of the said X-shaped members 30.and 31 extend, as isshown in Figs. 2 and'4 of theI drawings. As is clearly shown in Figure1, I preferably employ these X-shaped members in'pairs and in Figure 1will be seen an X-shapedmember 31 on each side of the upper transverseportion4 of the core, and as is clear from Figure 2, there isan X-shapedimember 30 on each side of the lower transverse portion 4 of the core. lAs already hereinabove noted, the fluid dielectric and cooling mediumwhich I prefer to use is a gas under pressure greater than atmosphericpressure and'with suoli a gasy ymagnetic circuit, space thevarious partsmore closelyy together, lessen the aniountof copper necessary and thusmaterially diminish the iron and copper losses and achieve betterregulation of the transformer. As illustrative of how such advantages asthe above are achieved, I might point out, forexample, that the space(see Figure 12) between vthe uppermost coil 20 of the `high tensionwinding and the upper transverse portion 4e of the transformer core isoccupied by the member 26 which is of solid dielectric mate- 'rial and alayer of gaseous dielectric under pressure. These two dielectrics arethus combined in series and the total dielectric stress is distributedbetween them inversely as their respective permittivities.

'lhepermittivity of solid dielectric material such as the bakelite ofthe member 26 is relatively high being on the order of 6, while thepermittivity of the gaseous dielectric'under pressure is relatively lowbeing substantially unity. Due to suoli characteristics as these and dueto the serial arrangement of the two dielectrics, I ain enabled to spacethe uppermost coil 2() of the high tension winding much more closely tothe portion leef the transformer core than would otherwise be possibleand, moreover, I am enabled also to use a much smaller thickness ofsolid dielectric, in such a relation, than would otherwise be necessaryfor the solid dielectric is made to assume a'relatively small Afractionl of the total stress while the great dielectric fl. similar seriesrelation betwen solid dielectric and the gaseous dielectric undei'pressure with resultant features of action and advantages like thoseabove-mentioned will be seen tojexist for insulating the high tensionwinding from the middle leg 4f of the transformer core, and by way offurther example will also be seen to exist for insulating adjacent coils20 of the high tension winding from each other. Thus, I am enabled toachieve better insulation between parts of the construction which are ofdifferent potentials, and I am also enabled to achieveV greatcompactnessof construction with other advantages thatwill be clear inview of what Has hereinabove been set forth.

As further conducive to a clearer understanding of certain otherfeatures of my invention, I might note that the gaseous dielectric underpressure coacts with the solid dielectric in still a further highadvantageous manner in that leakage along the solid dielectric materialis greatly reduced. Considering, for example, the sinuous soliddielectric membersl that extend between the adja- .cent coils 20 of thehigh tension winding (see the right-hand portion of Figure 2) it mightfirst be pointed out, as has already above been noted, that theconstruction of the members 16 greatly lengthens the leakage path fromone coil 20 to an adjacent coil 20, that is, the leakage path along thecurved or inclined portion or portions of the sinuous members 16. Thisfeature alone achieves many advantages, but in coaction with the gaseousdielectric under pressure the latter acts to prevent` leakage even alongsuch a lengthened inclined path and due to this action of the gaseousdielectric under pressure, I yam again enabledL much more closely tospace adjacent coils 2() of the high tension winding than wouldotherwise be possible.

Moreover, due to the conrmation of the sinnous members A16, the leakagepath available is along inclined paths which are of greater length thanthe spacing between the coils and hence is in a path of lower voltagegradient. Thus, leakage between adjacent coils of the high tensionWinding is effectively prevented while the spacing between the coils ismade much smaller than would otherwise be possible. The coaction ot thegaseous dielectric under pressure with the tubular member l5 of soliddielectric material and about which are supported the coils 20, will bebetter understood in view of the foregoing, but it may at thisl oint benoted that leakage along the mem er l5 between parts such as coils 2Othat are of different potential is effectively cut down, while theperforations 2l in themember l5 insure that any leakage paths betweentwo points of substantial spacing are longer than, the shortest"-distance between these two\ points.

It may also be noted at this point that the members 30 and' 31 whichsupport the high voltage winding structure are so shaped that ',theleakage path from the winding structure to the core structure (suchas'the angle iron members 3 or2 to which the members 30 and 3lrespectively are secured) is longer than the shortest distance. betweenthe winding structure and the angleiron members, and

the above-noted feature ofthe gaseous dielecof heat fromv such portionsand makes it possible to effectively 'guard against abnormal temperaturerises.

rlhe construction as shown in Figs. 3 to 5 inclusive is identical withthat shown in Figs. l and 2 of the drawings `except for certain featuresof construction, such as the provision in the laterally and outwardlyextending washers 16 of openings 35 at intervals therein, which openingsare situated practically or approximately one above the other,

' Y as shown in Fig. 4.

ln the construction, as shown in Figs. to inclusive, the respectivecoils 20 of the high `voltage winding are subdivided; that is, they aredivided into two parts a and 2Gb separated from each other by an annularpassageway 38 in which is situated a strip 40 of solid dielectric ofcorrugated oi' sinuous forni and which is of general circular fform, as

clearly shown in Figs. 3 `and 5. The outer wire. of the innersubd1vis1on 20h of each complete coil 2O situated between the washersI16 extends between the opposing adJaceutl ends of the annular strip 40and continuous forwardly upon the outer;A side of said strip to form theinner turn of the outer subdivision 20"L of each coil as indicated at 42in Fig. 5. lt will be noted that the outer vturns of wire of the innersubdivisions of the coils n l and the inner turns of wire of the outersubdivisions of the coils contact at intervals only with the said stripLl0, Ias is clearly shown 1n 4the-drawings. l

By reason of the prov1s1on of the open-v ings 35,Which are situated thesame distance radially from the axis of the tubular part l5 as are theannular spaces 38 between the in-` ner and outer subdivisions of thecoils 20, vertical ducts 36 are provided through the high Voltagewinding as shown. The corrugated or sinuous form of the separating stripbetween the subdivisions 20"L and 20b of the coils 20 will be seen to.substantially unobfluid dielectric and cooling medium within the tank ofthe transformer can freely pass through the vertical ducts 36 andwithdraw heat from the coil subdivisions with which it is thus broughtinto intimate thermal contact. This medium, as above noted, ispreferably a gaseous dielectric under pressure greater than atmosphericpressure.v

It will thus be seen that by reason of the employment of such featuresas the serial relation of solid dielectric material with a gaseousdielectric `under pressure for insulating the high tension winding fromthe horizontal portions 4 and le of the transformer core and theX-shaped members 30 and 3l for spacing and supporting the high voltagewinding structure in substantially the manner indicated in the drawings,a constructionl isv provided in which the distances between the endcoils and the horizontal portions of the core are less than would bepossible if the spaces between said coils and the said horizontalportions of the core were brid ed by solid dielectric material. As has aready been described hereinabove and is clearly indicated in the severalfigures of the drawings, the solid dielectrics 25 land 26 are in serieswith the tluid'diel'ectric between said end coils and said horizontalportions of the core. The coaction and advantages of this serialrelation where the fluid dielectric is a gas under pressure will beclearjand readily understood in view of what has hereinabove been setforth. lt will be seen, therefore, that on account of such features ofcoaction as above-noted and in which the high dielectric strength of thefluid dielectric and cooling medium where the latter is a gas underpressure, and the form of constructionLhereinbefore described andillustratively shown in the drawings, the core dimensions in the pathsof magnetic iuX are decreased. rlhe decrease in the core dimensions notonly makes possible the use of less iron in the magnetic circuit butalso eects a decreaseiin the iron losses. Also. the .closer spacingsmade possible between other portions of the transformer constructionwhich are of different, potential, all as have already hereinabove beenpointed out, makes possible the achievement of such advantages aslessening the from thel fact that a lower -temperature gradient betweenthe end coils and the Huid dielectric and cooling medium. is obtainedthan would be the case if the"` spaces between the end coils and thehorizontal portions of' the core were bridged by solid dielectric.

It will be understood that the transformer as illustrated is adapted tobe inclosed and supported within a hermetically sealed casing or tank,which, however, is not shown in the drawings.

In constructing the high voltage winding structure one of the annulardisks 25 or 26 will first be secured to the tubular part 15. If it beassumed that the disk 25 is iirst secured to the part 15 then the bottomcoil of thewinding will be wound upon the part 15, then a washer 16 willbe placed in position upon said coil with the part 15 projectingtherethrough, after which the next adjacent coil will be wound ripon thepart 15 and so on until the required number of coils have been woundafter which the annular disk 26 will be placed in position upon thetopmost coil and secured at its inner edge to lthe upper outer endportion of the part 15.

As many possible embodiments may be made of the above invention, and asmany changes might b-e made in the 'embodiment above set forth, it is tobe understood that all matter hereinbefore set forth is to beinterpreted as illustrative and not in a limiting sense.

Having-thus described my invention, what I claim and desire to secure byLetters Patent is:

1. In apparatus of the character described, in combination, a highvoltage winding for a transformer made up of a plurality of coilspositioned one above the other to form substantially a stack, and amember of solid dielectric material extending substantially lengthwiseof said stack of coils for holding the latter in substantial alinement,said member being provided with perforations shaped and positioned sothat a line drawn along the surface of said member in the generaldirection of the axis of said coils and between any two spaced points isgreater in length than the straight line distance between said twopoints, whereby the leakage path along vthe surface'of said member andin a general direction along which said coils make eifective apotential'diiference is other than in a ystraight line.

2. In apparatus of the character described, in combination, a highvoltage winding for a transformer made up of a plurality of coilspositioned one above the other to form substantially a stack, and amember .of solid dielectric material extending substantially lengthwiseof said stack of coils for holding ,the latter in substantial alinement,said member being provided with perforations shaped and positioned sothat a line drawn along the surface of said member in the generaldirection of the axis of said coils and between any two spaced points isgreater in length than the straight line distance between said twopoints, whereby the leakage path along the surface of said member and ina general direction along which said coils make effective a potentialdifference is other than in a straight line, anda gaseous dielectricunder pressure contacting said member and filling said perforations.

3. In apparatus of the characttfdescribed, i

in combination, a high voltage winding for a transformer made up of aplurality of coils positioned in spaced relation one above the other,and insulating means between adjacent coils comprising solid dielectricmaterial and a gaseous dielectric under pressure, said solid dielectricmaterial and said gaseous dielectric under pressure being combined so asto be in series in the path of higher voltage gradient between adjacentcoils and so that surface leakage along said solid dielectric andbetween adjacent coils is in a path or paths of lower voltage gradient.

4. In apparatus of the character described,

a transformer made up of a plurality of coils Aarranged in spacedrelation one above the other, means interposed between adjacent coilscomprising a corrugated member of solid dielectric material, said memberacting to hold adjacent coils in spaced relation and contact therewithonly at intervals, and a gaseous dielectric under pressure filling thespace between the corrugations of said solid dielectric member andadjacent coils whereby said corrugated imember and said gaseousdielectric under pressure are in series in the path of higher voltagegradient between adjacent coils and whereby any surface leakage betweenadjacent coils and along said solid dielectric member is yin a path orpaths of lower voltage gradient and whereby said adjacent coils may beclosely spaced.

5. lThe high voltage winding of an electric transformer, comprising aplurality of coils situated one above the other, a tubular memberof'dielectric material upon which said coils are wound, said tubularmember being provided with perforations, the centers of which arecoincident with the apices of substantially equilateral triangles andthe diameters of which are of such relation to the altitude of the saidtriangles that a straight line cannot be drawn, except for a limiteddislOl) tance, along the surface of the said tubular member from onepoint to another, and annular washer-like members of dielectric materialsituated between adjacent coils and contacting at intervals therewith tosupport the said coils in spaced relation to each other.

6. The high voltage winding of an electric transformer, comprising aplurality of coils situated one above the other, a tubular member ofdielectric material upon which said coils are wound, said tubular memberbeing provided with perforations, the centers of which are coincidentwith the apices of substantially equilateral triangles and-the diametersof which are of such relation to the altintu-de of the said trianglesthat a straight line cannot be drawn along the surface of the saidtubular member from one point to another, and annular washer-likesinuous members of dielectric material situated between-the said coilsand supporting the same in spaced relation with respect to each other.

7. lin apparatus of the character described, in combination, a highvoltage winding of anv electric transformer made up of a plurality ofcoils positioned in spaced relation one above the other, a substantiallytubular member of solid dielectric material upon which said coils arewound, substantially washershaped members ofsolid dielectric materialpositioned between adjacent coils for holding the latter in spacedrelation, said members being corrugated and extending in a directionaway from said substantially tubular member of solid dielectricmaterial, said last-mentioned member having apertures therein formingcommunications between the interior thereof and the spaces between thecorrugated members and coils spaced thereby,'and a gaseous dielectricvunder pressure filling said spaces and said apertures.

8. ln apparatus of the character described, in combination, atransformer core having a leg for receiving a winding and having aportion extending substantially transversely thereto, a highvoltagefwinding about saidl core leg, and means comprising asubstantially X-shaped member for supporting the end portion of saidwinding from said transversely extending portion of said core, wherebythe leakage path betweenthe end portion of said winding and along saidX-shaped member is materially greater than the shortest straight linedistance between the end portion of said winding and said transverselyextending portion of said core.

9. llhe high voltagewinding of a transformer, comprising a pluralityofcoils situated one above the other each of which coils is subdividedinto inner and outer portions, said portions beingseparated f rom eachother, a sinuous member substantially circular in outline situated inthe annular space between the said inner and outer portions of the saidcoils, sinuous washer members of dielectric material situated betweenthe said coils and 4supporting the same in spaced relation to eachother, and solid dielectric means for supporting the said coils andspacing means.

l0. The high voltage winding of a transformer, comprising a tubular partof dielectric material having annular disks situated at the upper andlower end portions thereof, coils wound upon the said tubular part,which coils -are situated one above the other, and each of which issubdivided into inner and outer portions, which portions are separatedby an annularspace, sinuous strips of dielectric material situated insaid spaces and contactingat intervals with the turns of the saidwindings being concentric and the primary winding being located inwardlyof the secondary winding, a tubular support for the secondary winding,the said support inclosing the primary winding and being lspaced'therefrom and-also being provided with perforations, and annularcorrugated washerlike members of dielectric material located between thesecondary windings, the alternate groovesand ridges formed by saidcorrugations extending radially from the'axis of the said transformer.

i2. ln apparatus of the character described, in combination, atransformer' core having a leg for receiving a winding and having aportion extending substantially transversely thereto; a high voltageWinding about said core leg; means for insulating said winding from saidtransverse portion of said core, said means comprising solid dielectricmaterial and a gaseous dielectric under pressure in series with saidsolid dielectric material across the` space between the end portion ofsaid windingr and said transverse portion of said core; andv meansextraneous of the space between the end portion of said winding and saidtransverse portion of said core for holding said winding relative to thelatter.

i3.- ln apparatus of the character scribed, in combination, a highvoltage winding having relatively adjacent portions thereof lengthwiseof its axis at different potentials, and a member of solid dielectricmaterial extending along said portions of the winding for mechanicallyholding the latter, said member being provided with perforations shapedand positioned so that a line drawn along the surface of said member inthe general direction of the axis of said winding and between any twospaced points is greater in length than the straight line distancebetween said two points, whereby the leakage path along the surface ofsaid member and in a general direction along which said portions of thewinding make effective a potential difference is other than in astraight line.

14. ln apparatus of the character described, in combination, a highvoltage windinghaving relatively adjacent portions thereof lengthwise ofits axis at different potentials, and a'member of solid dielectricmaterial extending along said portions of the de- Y winding formechanically holding the latter, said member being provided withperforations shaped and positioned so that a line drawn along thesurface of said member in the general direction ofthe axis of saidwinding and between any two spaced points is greater in length than thestraight line distance between said two points, whereby the leakage pathalong the surface of said member and in a general direction along whichsaid portions of the winding make effective a potential difference isother than in a straight line, and a gaseous dielectric under pressurecontacting said member and filling saidfperforations. y y

15. In apparatus of the character described, in combination, a highvoltage winding of an electric transformer made up of a plurality` ofcoils positioned in spaced relation one above the other, a substantiallytubular member of solid dielectric material about which said coilsextend, and insulating means between -adjacent coils comprising soliddielectric material and a gaseous dielectric under pressure, said soliddielectric material and said gaseous dielectric under pressure beingcombined so as tobe in series in the path of higher voltage gradientbetween adjacent coils and so that surface leakage along said soliddielectric and between adjacent coils is in a path or paths of lowervoltage gradient, said tubular member being provided with perforationsshaped and positioned so that a line drawn along the surface of saidmember in the general direction of the axis of said coils and betweenany two spaced points is greater in length than 'the straight linedistance between said two points.

1G. In apparatus ofthe ch'aracter described, in combination, atransformer core having a leg for receiving a winding and having aportion extending substantially transversely thereto; a high voltagewinding about said core leg and having its end port'ion spaced from saidtransverse core por; tion; and means for insulating said winding fromsaid transverse core portion and for supporting said winding from saidcore, said means including a member of solid dielectric material restingagainst the end of said winding and having a lesser thickness than thespacing between said end portion of the winding and said transverse coreportion, a gaseous dielectric under pressure interposed between saidsolid dielectric member and said transverse core portion so that saidtwo dielectrics are in series, and means secured to said core andengaging said solid dielectric member extraneously ,of the space betweenthe latter and said transverse core portion for holding said winding inplace.

17. In a transformer, in combination, a high Voltage winding, a lowvoltage member in the form of a low voltage winding, a core member withwhich said windings coact, said high voltage winding being spaced from`both of'said members; and means for insulating said high voltagewinding from one of said members, said means including a layer of soliddielectric material and a layer of gaseous dielectric under pressure inthe space between said high voltage winding and said one of saidmembers. v18. In a transformer, in combination, a transformer coremember, a coil member about said core member, another coil member aboutsaid core member and adapted to operateat a Voltage relatively higherthan that of said first-mentioned coil member and lspaced from both ofsaid other members, and means for insulating said relatively highervoltage member from one of said other members, said means comprisingsolid dielectric material and a gaseous dielectric under pressure, bothof said dielectrics being in the space between said members to beinsulated and being combined so as to be in series in the patli ofhigher voltage gradient between said members to be insulated and so that'surface leakage along said solid dielectric between said members-is ina path or paths of lower voltage gradient.

In testimony that I claim the foregoing as my invention I have hereuntosigned my name this 4th day of March, 1922.

FRANKLIN S. SMITH.

